1. Field of the Invention
This invention relates to a method and apparatus for mixing and dispensing fluids which react with each other. The mix cylinder, piston and orifices of a foam gun are flushed and cleaned at the end of each dispensing operation. The invention is particularly useful for mixing organic resins and polyisocyanates to dispense polyurethane foam. The dispensing gun may also dispense a single fluent material.
2. Description of Background and Relevant Information
The forming of synthetic foams, such as polyurethane foams, requires uniform mixing of liquid organic resins and polyisocyanates. A problem that occurs in such mixing is that the organic resin and polyisocyanate react relatively rapidly and accumulate over the surfaces of the dispensing apparatus. The foam increases in volume and may block passages within the foam gun and the feed hoses leading to the gun. This disables the foam gun, which must then be replaced, leading to down-time and excessive cost.
U.S. Pat. No. 4,426,023 to SPERRY et al. discloses a foam gun in which a cleaning assembly supplies a solvent to the discharge part of the foam gun and a valving rod of a piston travels through a solvent reservoir. This cleaning assembly cleans the discharge port and the valving rod but does not adequately clean the orifices through which the organic resins and polyisocyanates are supplied.
U.S. Pat. No. 4,159,079 to PHILLIPS, Jr. discloses a foam dispenser which includes gaskets to prevent the emigration of liquids from the mixing chamber. The mixing chamber is press fit inside the bore of the front section of the foam gun. The valving rod is bathed in a cleaning and/or lubricating solvent in a chamber.
U.S. Pat. No. 4,568,003 to SPERRY et al. discloses a foam dispenser in which the mixing chamber is detachable to facilitate cleaning.